Thanks for the responses, but I'm not trying to disable the windows sounds, I'm trying to prevent them from being disabled.
I guess I don't really understand how this can work. If you select "Do not use audio features" for a sound controller in the device manager, how can it be available to programs in windows?
I've tried this with my old desktop with an audigy 2zs pci card and an m-audio audiophile usb external device, and basically it just disables the device in windows, making it no longer available to foobar or any other app. If I select "Do not map to this device" but leave the "use audio features" on, then it works, and it does seem to bypass the kmixer, using either the creative mixer, or the maudio mixer instead.
Am I missing something?
BTW - while I was experimenting with this, I also compared foobar 0.9.x to 0.8.3 (per Steve's suggestion) and boy it is a pretty big difference. It is unfortunate that a lot of the new interface plugins don't work on 0.8.3, but I'll happily sacrifice those for better sound.